1. Field of the Invention
This invention relates in general to bedding, namely, mattresses and box springs. More particularly, this invention relates to stress-relieving treatment of coil springs for placement in pocketing material for subsequent use in mattresses or box springs.
2. Description of Related Art
It is known to form wire into individual coil springs and to combine such coil springs into a single innerspring unit which may be used as a mattress or as a box spring.
It is also known to provide individually "pocketed" coils and to assemble such pocketed coils into innerspring constructions for later upholstery into mattresses or box springs. An example of a method and apparatus for assembling such pocketed coil springs is shown in U.S. Pat. No. 4,439,977 to Stumpf, which is incorporated herein by reference. Methods and apparatus for combining groups of pocketed coils into a unitary string or array of coils for installation as innerspring units within a mattress assembly as illustrated in U.S. Pats. Nos. 4,578,834, and 4,986,518 which also are incorporated by herein reference.
Although the above systems provide several advantages over prior constructions, a need for improvement still exists. For example, when coils are compressed for insertion into pockets as shown in U.S. Pat. No. 4,439,977, the coils may tend to "set" resulting in a disadvantageous permanent height or load loss. Disadvantages also exist in that the wire tends to undergo certain stresses during formation which may cause residual faults in the coil springs.
Therefore, a need has been recognized in the industry to provide springs which do not exhibit stress induced problems including disadvantageous "set" conditions.
General heat treatment of coil springs is known. For example, it is known to provide "open-coil" innerspring constructions, and then to place such open coil innerspring constructions into an oven for stress relief. However, in the instance of innerspring constructions of pocketed coils, such constructions do not lend themselves to oven-heating since, for example, the pocket fabric or the glue holding the pocketed coil springs together will degrade if subjected to high temperatures as will be encountered with oven heating.
Therefore, a need has been recognized to provide a method and apparatus for providing improved pocketed coils and innerspring constructions made therefrom and to the products produced thereby.